The occurrence and severity of fireblight (Erwinia amylovora), apple scab (Venturia inequalis), cedar rust diseases (Gymnosporangium sp.), powdery mildew (Podosphaeria leucotricha) and frogeye leaf spot (Botryosphaeria obtusa) were assessed on 60 cultivars of flowering crabapple (Malus sp.) in Brewton, AL (Plant Hardiness Zone 8). Of these diseases, fireblight was the most widespread and damaging over the four-year test period. Noticeable and sometimes damaging levels of frogeye leaf spot and apple scab were seen on a few select crabapple cultivars. Surprisingly, none of the cedar rust diseases commonly found in Alabama on members of the apple family caused significant damage. The signs or symptoms of powdery mildew were never seen on any of the 60 crabapples. Of the crabapple cultivars screened, ‘Eleyi’, ‘Radiant’, ‘Adams’ dwarf, and ‘Velvet Pillar’ had the highest survival rates, as well as resistance to fireblight and frogeye leaf spot. However, ‘Radiant’ and, particularly, ‘Eleyi’ are sensitive to apple scab and may suffer considerable damage in landscape plantings where the climate is cooler. ‘Red Splendor’ dwarf and M. baccata cv. ‘Jackii’ were also highly disease resistant but did not have good rates of survival. Oxysporus root and collar rot (O. latemarginatus) killed many trees and was most prevalent in poorly drained areas found behind several low terraces. On the basis of the high risk of disease and poor overall survival rate, the majority of crabapples tested cannot be considered well adapted to the Gulf Coast region of Alabama nor to adjoining states.
2Professor and Extension Specialist, Department of Entomology and Plant Pathology.
3Professor and Associate Professor, respectively, Department of Horticulture.
4Superintendent, Brewton Experiment Field.